Oil filler nut



FIG. 1 is a side elevational view of an oil filler nut showing my new design;

FIG. 2 is a top plan view;

FIG. 3 is a bottom plan view; and,

FIG. 4 is a side elevational view, the broken line showing of an engine oil filler is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for an oil filler nut, as shown. 